Low free formaldehyde phenolic polyol formulation

Abstract

A resin is prepared by the reaction of a phenol, an aldehyde and an aliphatic hydroxy compound containing two or more hydroxy groups per molecule in the presence of a divalent metal ion catalyst. These resins react with polyisocyanates to form polyurethanes that are useful binders for foundry cores and molds.

What is claimed is: 
     
       1. A method for preparing a modified orthobenzylic ether-containing resole resin which comprises the steps: (a) reacting a phenol in the presence of a divalent metal ion catalyst at a pH below about 7 with a molar excess of an aqueous aldehyde;   (b) adding to the reaction mixture of step (a) from about 0.001 to about 0.03 mole of an aliphatic hydroxy compound per mole of phenol when from 0% to about 85% of the aldehyde has reacted;   (c) reacting the mixture of step (b) until from about 80% to about 98% of the aldehyde has reacted; and   (d) heating the reaction mixture of step (c) under vacuum until the amount of free formaldehyde in the mixture is less than about 1% by weight, wherein the aliphatic hydroxy compound added in step (b) contains two or more hydroxy groups per molecule and has a hydroxyl number of from about 200 to about 1850.     
     
     
       2. The process of claim 1, wherein steps (a) and (c) are carried out under reflux. 
     
     
       3. The method of claim 1, wherein the aliphatic hydroxy compound added in step (b) is selected from the group consisting of ethylene glycol propylene glycol, 1,3-propanediol, diethylene glycol, triethylene glycol, glycerol, sorbitol and polyether polyols having a hydroxyl number from about 200 to about 1850. 
     
     
       4. The method of claim 1, wherein the phenol is unsubstituted phenol and wherein the aldehyde is formaldehyde. 
     
     
       5. The method of claim 1, wherein the divalent metal ion catalyst used in step (a) is zinc acetate. 
     
     
       6. The method of claim 1, wherein the aliphatic hydroxy compound is added in step (b) when from about 50% to about 80% of the aldehyde has reacted. 
     
     
       7. A method for preparing a modified orthobenzylic ether-containing resole resin which comprises the steps: (a) reacting a phenol in the presence of a divalent metal ion catalyst at a pH below about 7 with a molar excess of an aqueous aldehyde and at least about 0.25 mole of a monohydric alcohol per mole of phenol;   (b) adding to the reaction mixture of step (a) from about 0.001 to about 0.03 mole of an aliphatic hydroxy compound per mole of phenol when from 0% to about 85% of the aldehyde has reacted;   (c) reacting the mixture of step (b) until from about 80% to about 98% of the aldehyde has reacted; and   (d) heating the reaction mixture of step (c) under vacuum until the amount of free formaldehyde in the mixture is less than about 1% by weight, wherein the aliphatic hydroxy compound added in step (b) contains two or more hydroxy groups per molecule and has a hydroxyl number of from about 200 to about 1850.     
     
     
       8. The process of claim 7, wherein steps (a) and (c) are carried out under reflux and step (d) is heated at a temperature up to about 95° C. 
     
     
       9. The process of claim 7, wherein the monohydric alcohol added in step (a) is methanol. 
     
     
       10. The process of claim 7, wherein the aliphatic hydroxy compound added in step (b) is selected from the group consisting of ethylene glycol, propylene glycol, 1,3-propanediol, diethylene glycol, triethylene glycol, glycerol, sorbitol and polyether polyols having a hydroxyl number from about 200 to about 1850. 
     
     
       11. The process of claim 7, wherein the phenol is unsubstituted phenol and wherein the aldehyde is formaldehyde. 
     
     
       12. The process of claim 7, wherein the divalent metal ion catalyst used in step (a) is zinc acetate. 
     
     
       13. The process of claim 7, wherein the aliphatic hydroxy compound is added in step (b) when from about 50% to about 80% of the aldehyde has reacted.